It's a little difficult to unpick your friends symptom's here, and I guess even an ent consultant would find it hard to predict the affect of air travel on his condition, but it's probably fair to say that effect would be short lived.
If it's so disabling, it'd be worth getting a specialist opinion for two reasons, firstly to calm your friends percieved fears, and secondly because modern treatments tend to be very effective.
In my friends case I believe he was subject to a ham fisted and dangerous procedure by a, probably, incompetent doctor who did significant and permanent damage. Today he could have sued but then what price loss of hearing?
I can sympathise with your palpable anger, but we can only work with the knowledge we've got at the time, which, at the time, told us that the best thing we could do for patients with wax in their ears was to syringe them. I used to enjoy syringing ears' it's one of the few times we get to cure patients. Now we know better !!
In what way was your friends doctor ham fisted? And would he be sued if, at the time, he acted reasonably?